that NPCs are also movers and shakers in the game world, not just game elements that behave in a reactive manner.
From within the context of the game world, sure, but the game world exists a backdrop for the characters' activities. It's all reactive. Even when things the players don't know anything about, yet, are happening in the background, it's a consequence of the PCs ignoring them or having not uncovered them sooner. ;P
...A pretty fine distinction, I know.
Completely different sub-topic: Intimidation. I get the sense that we're mostly looking at Intimidate as a sort of non-magical fear effect. As I said before, I think that's missing some of the nuance of it as a CHA based skill. If it were just being fearsome, your size, appearance, and ability to demonstrate overwhelming power would be all that mattered. But it's not that, it's using fear to manipulate someone. You have to create fear, or at least pragmatic concern, but also leave an out, an action the subject can take or refrain from that credibly removes the threat, and present reason to think that compliance will bring some modicum of safety. A successful check would thus be that complete package: the intimidator has created the impression that he's a serious threat, but that he can be trusted not to carry through if he's given what he wants. If the target's left thinking "he'll kill me anyway" or "or maybe I can get away" or "I don't know what he wants" - that's a failed intimidate, too, no matter how scared he may be.'
It also needn't be fear of the character making the check - when I call for an intimidate check, it's not always because the player is having his character make a threat or loom menacingly or anything like that. It's can also be when they're offering aid or protection or seeking an alliance. "You should work with us against Fangthane the Render, because he and his horde represent an immediate danger to your community." It's not a direct threat, but it plays on fear and relies on the PC being formidable.
Another not too closely related sub-topic: 5e's basic example of play, what I consider it's core resolution system in a technical sense, is player driven. Player declares an action, the DM narrates the results of the action. Earlier I asked if an NPC intimidating a player really fit that. Now I'll go out on a limb and say that it doesn't. Rather, the player will do something that will lead to an interaction with an NPC, that might involve the NPC trying to intimidate (or deceive or whatever) and the DM would take that into account in narrating the results of the PC's action, including, possibly, a check or opposed check. Just how I'd see it working in 5e.